What are the Constitutional limitations on Congress' authority to act?

The Constitution lists specific powers given to Congress to pass laws. This is called "enumerated powers." For any law Congress passes, they have to point to where in the Constitution they are given that power. If it's not expressly written in the Constitution, then Congress has to show that the power to pass that law is implied by other powers listed. The purpose of this rule is to limit the power of the Federal Government and prevent Congress from overreaching. The Founders wanted checks on Federal power to protect people's rights and liberties. So the Constitution only gives Congress certain limited powers, while everything else is left to the states or individuals. This rule forces Congress to restrain itself and makes sure new laws adhere to the Constitution's grants of authority.